1. Field of the Invention:
The present invention relates to a photosensitive member of the function-separated type comprising an evaporated film of phthalocyanine compounds as a charge generating layer and a hydrogen-containing amorphous carbon layer as a charge transporting layer.
2. Description of the Prior Art:
Remarkable progress has been made in the application of electrophotographic techniques since the invention of the Carlson process. Various materials have also been developed for use in electrophotographic photosensitive members.
Conventional photoconductive materials chiefly include inorganic compounds such as amorphous selenium, selenium-arsenic, selenium-tellurium, zinc oxide, amorphous silicon and the like, and organic compounds such as polyvinylcarbaxole, metal phthalocyanine, dis-azo pigments, tris-azo pigments, perillene pigments, triphenylmethanes, triphenylamines, hydrazones, styryl compounds, pyrazolines, oxazoles oxadiazoles and the like. The structures of photosensitive members include, for example, those of the single-layer type wherein such a material is used singly, the binder type wherein the material is dispersed in a binder, and the function-separated type comprising a charge generating layer and a charge transporting layer.
However, conventional photoconductive materials have various drawbacks. For example, the above-mentioned inorganic materials except for amorphous silicon (a-Si) are harmful to the human body.
The electrophotographic photosensitive member, when employed in a copying apparatus, must always have stabilized characteristics even if it is subjected to the severe environmental conditions of charging, exposure, developing, image transfer, removal of residual charges and cleaning. However the foregoing organic compounds have poor durability and many unstable properties.
In order to eliminate these drawbacks, progess has been made in recent years in the application of a-Si formed by the glow discharge process to electrophotographic photosensitive members as a material with reduced harmfulness, higher sensitivity, higher hardness such as more than 7H level of the JIS standards for pencil lead hardness and higher durability. Nevertheless, a-Si material is hazardous to manufacture since it requires highly ignitable silane gas as its starting material. Moreover, a-Si requires a large quantity of silane gas which is expensive, rendering the resulting photosensitive member much more closely than conventional photosensitive members. The manufacture of photosensitive members of a-Si involves many other disadvantages, for example, a-Si has a low film-forming speed and releases a large amount of explosive undecomposed silane products in the form of particles when forming a film. Such particles, when incorporated into the photosensitive member being produced, gives seriously adverse influences on the quality of images obtained. Further, a-Si has a low chargeability due to its original high relative dielectric constant. This necessitates the use of a charger of higher output to charge the a-Si photosensitive member to a predetermined surface potential in the copying apparatus.
It is conventionally known that the evaporated film formed from phthalocyanine compounds can be employed as a charge generating layer in a photosensitive member. In the Journal of Non-Crystalline Solid, Vol. 6, pp. 13-26, 1971, for example, P. J. Regensburger and N. L. Petruzzella state that a photosensitive member comprising a charge generating layer of an evaporated film of metal-free phthalocyanine and a charge transporting layer of amorphous selenium exhibits desirable light decay.
Many inventions are directed to an evaporated film of phthalocyanine applicable as a charge generating layer. At the same time, many inventions concern charge transporting materials which are excellent in adhesivity, charge transportability and charge injection from a charge generating layer which functions as an excellent photosensitive member by lamination to the above-mentioned charge generating layer.
For example, U.S. Pat. No. 3,895,944 discloses a photosensitive member which comprises an evaporated film of phthalocyanine either metal-free or containing metal such as Cu, Cd, Zn, Pb and the like, as a charge generating layer, and a charge transporting layer of oxidiazole coated on the evaporated film.
Japanese Unexamined Patent Publication No. SHO 49-11136 discloses a photosensitive member which comprises an evaporated film of phthalocyanine either metal-free or containing metal such as Cu, Ni, Co and the like, formed on a resin layer of low resistance and serving as a charge generating layer, and an organic photoconductive material such as poly-N-vinylcarbazole, polyacenaphthylene, poly-9-vinylacridine and the like, is coated thereon as a charge transporting layer.
U.S. Pat. No. 3,992,205 disclosed a photosensitive member which comprises a charge generating layer having an evaporated layer of metal-free or Cu phthalocyanine and another evaporated layer of other coloring agent in a laminated structure, and an organic material such as N-vinylcarbazole, pyrazoline and the like is coated on the charge generating layer as a charge transporting layer.
Japanese Unexamined Patent Publication No. SHO 57-20741 discloses a photosensitive member comprised of evaporated film of Cu phthalocyanine, as a charge generating layer, and an organic compound, such as pyrazoline, N-carbazole and the like, is coated thereon as a charge transporting layer.
Japanese Unexamined Patent Publication No. SHO 57-148745 discloses a photosensitive member which comprises an evaporated film of phthalocyanine containing metal, such as Al, Cr, Ga, Sb, In, Si, Ti, Ge, Sn, Te and the like, as a charge generating layer, and an organic compound, such as pyrazoline, carbazole and the like, coated thereon as a charge transporting layer.
U.S. Pat. NO. 4,426,434 discloses a photosensitive member which comprises an evaporated film of phthalocyanine as a charge generating layer containing Al as a metal and Cl as a substitute (AlPc, AlClPc, AlClPc(Cl)), and an organic compound of pyrazoline is coated thereon as a charge transporting layer, the evaporated film being treated by a solvent such as THF, acetone and the like.
These disclosed inventions are all directed to a photosensitive member wherein a charge transporting layer comprising organic charge transporting material is coated on an evaporated film of phthalocyanine compounds. Photosensitive members of this structure have low hardness, since the surface of the members is formed of an organic coated film, showing hardness of only 5B to 2B level of the JIS standards for pencil lead hardness. Therefore, such photosensitive members, when used in a copying apparatus, have low wear and abrasion resistance against contact with the developing device, transfering device, cleaning device and the like, showing poor durability. Moreover, the evaporated film of phthalocyanine may be altered by the solvent used for coating, thereby affecting the photosensitive characteristics, especially the spectral sensitivity characteristics. This may limit the effective use of the evaporated film of phthalocyanine. Additionally, the photosensitive members are prepared by applying the evaporated film in a vacuum, and then, coating the organic charge transporting layer thereon outside the vacuum chamber. From the manufacturing viewpoint the above-mentioned process is a complicated one.
Japanese Unexamined Patent Publication No. SHO 55-29844 discloses a photosensitive member comprising an evaporated film of phthalyocyanine, containing metal such as Cu, Ni, Fe, Mg, Al and the like, as a charge generating layer, and a film formed from an organic compound of pyrazoline coated thereon as a charge transporting layer. The charge transporting layer is coated by evaporation, sputtering and ion plating method.
By this process, the photosensitive members having relatively high hardness up to the H to 2H level according to JIS standards for pencil lead hardness, can be obtained. However, compared to the amorphous silicon described above, such members are not hard enough. Further, the coating method reduces the charge transportability of pyrazoline compounds having inherently suitable hole transportability. Consequently, suitable sensitivity cannot always be obtained.
Moreover, the above disclosure about function-separate photosensitive members using an evaporated film of phthalocyanine as a charge generating layer do not solve the substantial problems described above inherent to a-Si.
On the other hand, it has been proposed in recent years to use amorphous carbon films as plasma-polymerized organic films for photosensitive members.
Plasma-polymerized organic films per se have been well-known for a long time. In Journal of Applied Polymer Science, Vol. 17, pp. 885-892, 1973, for example, M. Shen and A. T. Bell state that a plasma-polymerized organic film can be produced from the gas of any organic compound. The same authors discuss film formation by plasma polymerization in "Plasma Polymerization," published by the American Chemical Society in 1979.
However, the plasma-polymerized organic films prepared by the conventional process have been used only as insulating films. They are thought to be insulating films having a specific resistivity of about 10.sup.16 ohm-cm, like usual polyethylene films, or as used are recognized at least as such. The use of this film with electrophotographic photosensitive members is based also on the same concept; the film has found only limited use as an undercoat or overcoat serving solely as a protective layer, adhesion layer, blocking layer or insulating layer.
For example, Unexamined Japanese Patent Publication SHO 59-28161 discloses a photosensitive member which comprises a plasma-polymerized high polymer layer of reticular structure formed on a substrate and serving as a blocking-adhesion layer, and an a-Si layer formed on the polymer layer. Unexamined Japanese Patent Publication SHO 59-38753 discloses a photosensitive member which comprises a plasma-polymerized film having a thickness of 10 to 100 angstroms and formed over a substrate as a blocking-adhesion layer, and an a-Si layer formed on the film, the plasma-polymerized film being prepared from a gas mixture of oxygen, nitrogen and a hydrocarbon and having a high resistivity of 10.sup.13 to 10.sup.15 oh-cm. Unexamined Japanese Patent Publication SHO 59-136742 discloses a photosensitive member wherein an aluminum substrate is directly coated with a carbon film having a thickness of about 1 to about 5 .mu.m and serving as a protective layer for preventing aluminum atoms from diffusing through an a-Si layer formed over the substrate when the member is exposed to light. Unexamined Japanese Patent Publication SHO 60-63541 discloses a photosensitive member wherein a diamond-like carbon film, 200 angstroms to 2 .mu.m thick, is interposed between an aluminum substrate and an overlaying a-Si layer to serve as an adhesion layer to improve the adhesion between the substrate and the a-Si layer. The publication says that the film thickness is preferably up to 2 .mu.m in view of the residual charge.
The above disclosed inventions are all directed to a so-called undercoat provided between the substrate and the a-Si layer. In fact, these publications mention nothing whatever about charge transporting properties, nor do they offer any solution to the foregoing substantial problems with a-Si.
Furthermore, U.S. Pat. No. 3,956,525, for example, discloses a photosensitive member of the polyvinylcarbazoleselenium type coated with a polymer film having a thickness of 0.1 to 1 .mu.m and formed by glow discharge polymerization as a protective layer. Unexamined Japanese Patent Publication SHO 59-214859 discloses a technique for protecting the surface of an a-Si photosensitive member with an approximately 5-.mu.m-thick film formed by plasma-polymerizing an organic hydrocarbon monomer such as styrene or acetylene. Unexamined Japanese Patent Publication SHO 60-61761 discloses a photosensitive member having a diamond-like carbon thin film, 500 angstroms to 2 .mu.m thick and serving as a surface protective layer. Preferably the film thickness is up to 2 .mu.m due to trasmittancy. Unexamined Japanese Patent Publication SHO 60-249115 discloses a technique for forming a film of amorphous carbon or hard carbon with a thickness of about 0.05 to about 5 .mu.m for use as a surface protective layer. The publications states that the film adversely affects the activity of the protected photosensitive member when exceeding 5 .mu.m thick.
The above disclosed inventions are all directed to a so-called overcoat formed over the surface of the photosensitive member. The publications disclose nothing whatever about charge transporting properties, nor do they solve the aforementioned substantial problems of a-Si in any way.
Unexamined Japanese Patent Publication SHO 51-46130 discloses an electrophotographic photosensitive member of the polyvinylcarbazole type which has a polymer film 0.001 to 3 .mu.m thick and formed on its surface by being subjected to glow discharge polymerization. Nevertheless, the publication is totally mute about charge transporting properties, further failing to solve the foregoing substantial problems of a-Si.
Thus, the photosensitive members employing the conventional evaporated films of phthalocynine as a charge generating layer exhibit low surface hardness, poor durability and poor sensitivity due to the limited combination with a charge transporting layer.
On the other hand, the conventional plasma-polymerized organic films for use in electrophotographic photosensitive members are used as undercoats or overcoats because of their insulating properties and need not have a carrier transporting function. Accordingly, the films used are of limited in thickness, up to about 5 .mu.m at the largest. Carriers pass through the film owning to a tunnel effect, while if the tunnel effect is not expected, the film used has such a small thickness that it will not pose actual residual potential problems.